Exposure apparatus

ABSTRACT

An exposure apparatus includes a projection optical system for projecting a pattern on a reticle onto an object to be exposed, a reference mark that serves as a reference for an alignment between the reticle and the object, a first fluid that has a refractive index of 1 or greater, and fills a space between at least part of the projection optical system and the object and a space between at least part of the projection optical system and the reference mark, and an alignment mechanism for aligning the object by using the projection optical system and the first fluid.

BACKGROUND OF THE INVENTION

The present invention relates generally to an exposure apparatus, andmore particularly to an exposure apparatus used to manufacture variousdevices including semiconductor chips such as ICs and LSIs, displaydevices such as liquid crystal panels, sensing devices such as magneticheads, and image pickup devices such as CCDs, as well as fine patternsused for micromechanics. The present invention is suitable, for example,for an immersion type exposure apparatus that immerses, in the fluid,the final surface of the projection optical system and the surface ofthe object to be exposed, and exposes the object through the fluid.

Conventionally employed reduction projection exposure apparatuses use aprojection optical system to project or transfer a circuit pattern on amask or a reticle onto a wafer, etc., in manufacturing such a finesemiconductor device as a semiconductor memory and a logic circuit inthe photolithography technology.

The critical dimension transferable by the projection exposure apparatusor resolution is proportionate to a wavelength of light used forexposure, and inversely proportionate to the numerical aperture (“NA”)of the projection optical system. The shorter the wavelength is, thebetter the resolution is. Smaller resolution has recently been requiredwith a demand for the finer processing to the semiconductor devices.Therefore, in addition to use of the exposure light with a smallwavelength, the projection optical system is expected to improve theresolution by using a higher NA. At present, the projection opticalsystem has accelerated an increase of its NA, and it is expected todevelop the projection optical system having a NA of 0.9 or greater.

On the other hand, the light sources for the exposure apparatus havechanged from a KrF laser (with a wavelength of 248 nm) to an ArF laser(with a wavelength of 193 nm) Currently, developments of an F₂ laser(with a wavelength of 157 nm) and EUV (with a wavelength of 13.5 nm) arepromoted for the next generation light sources.

With this background, an immersion exposure has attracted attentions asa method that uses the ArF laser and the F₂ laser for more improvedresolution. See, for example, Japanese Patent Application, PublicationNo. 10-303114. The immersion exposure arranges the fluid as a medium ata wafer side of the projection optical system (or an image surfaceside), and promotes a higher NA. Specifically, the projection opticalsystem's NA is n·sin θ where “n” is a refractive index of the medium,which can be increased up to “n” by filling the medium (fluid) having arefractive index greater than that of the air, i.e., n>1, in at leastpart of the space between the projection optical system and the wafer.In other words, the immersion exposure improves the resolution byincreasing the projection optical system's NA viewed from the wafer sideup to 1 or greater.

On the other hand, in order to align the reticle with the wafer duringthe exposure, the exposure apparatus includes plural alignment opticalsystems. The alignment optical system is roughly classified into twotypes, i.e., an off-axis alignment optical system that detects analignment mark on the wafer and uses it for the alignment for the wafer,and a through the reticle (“TTR”) alignment optical system that detects,via the projection optical system, a position of the alignment mark onthe wafer (or wafer-side reference plate provided on a wafer stage),which is referred to as a wafer-side pattern and corresponds to areticle-side pattern that is an alignment mark on the reticle (orreticle-side reference plate provided on a reticle stage). The TTRalignment optical system is also referred to as a through the lens(“TTL”) alignment optical system.

Since the immersion type exposure apparatus fills the fluid in the spacebetween the projection optical system and the wafer so as to implementthe NA of 1 or greater, there is no imaging relationship between thereticle-side pattern and the wafer-side pattern in the TTR alignmentoptical system. As a result, the light intensity detecting method fordetecting the light intensity using a light intensity sensor provided onthe wafer stage, and then a positional relationship between thereticle-side pattern and the wafer-side pattern, can neither image thereticle-side pattern on the wafer-side pattern nor precisely align thereticle-side pattern with the wafer-side pattern. On the other hand, animage detecting method that images an alignment mark on an image pickupdevice cannot image the wafer-side pattern on the image pickup devicevia the projection optical system, or align the reticle-side patternwith the wafer-side pattern.

The light intensity detecting method has an area that has a refractiveindex of 1, such as the air and vacuum, between the wafer-side referenceplate and the light intensity sensor. When reticle-side pattern isimaged on the wafer-side pattern by using the light having the NAgreater than 1, the light having the NA greater than 1 is totallyreflected on the back surface of the wafer-side reference plate, whichback surface opposes to the pattern surface, and does not reach thelight intensity sensor. Therefore, a correct measurement value cannot beobtained due to offsets of the measurement values and the deterioratedmeasurement reproducibility. On the other hand, the light having the NAsmaller than 1 is not totally reflected on the back surface of thewafer-side reference plate, but the reflectance becomes higher due tothe large incident angle. Therefore, disadvantageously, the light havinga high NA is reflected on the back surface of the wafer-side referenceplate and its light intensity incident upon the light intensity sensoris smaller than that of the light having a small NA. The image detectingmethod that requires the illumination light to enter the back surfaceside of the wafer-side reference plate cannot use the incident lighthaving a NA greater than 1, due to the area that has a refractive indexof about 1 between the wafer-side reference plate and an emittingsection that emits the illumination light.

A non-immersion type exposure apparatus has a similar problem that thelight having a large NA is reflected on the back surface of thewafer-side reference plate, due to the higher NA used for the projectionoptical system. In order to receive the light having an arbitrary NA, asensor needs to have a large area and, when a light intensity sensorhaving a large area is provided on the wafer stage, the wafer stagebecomes too large.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an exemplary object of the present invention toprovide an exposure apparatus that employs a projection optical systemthat has a high NA (such as an immersion type or 1<NA), and providesprecise alignments and exposures with a good resolution withoutincreasing the size of the apparatus.

An exposure apparatus according to one aspect of the present inventionincludes a projection optical system for projecting a pattern on areticle onto an object to be exposed, a reference mark that serves as areference for an alignment between the reticle and the object, a firstfluid that has a refractive index of 1 or greater, and fills a spacebetween at least part of the projection optical system and the objectand a space between at least part of the projection optical system andthe reference mark, and an alignment mechanism for aligning the objectby using the projection optical system and the first fluid.

An exposure apparatus according to another aspect of the presentinvention includes a projection optical system for projecting a patternon a reticle onto an object, a reference mark that serves as a referencefor an alignment between the reticle and the object, a light-receivingelement for receiving light that transmits the reference mark, and afluid that has a refractive index of 1 or greater, and fills a spacebetween the reference mark and the light-receiving element.

An exposure apparatus according to another aspect of the presentinvention includes a projection optical system for projecting a patternon a reticle onto an object, a reference mark that serves as a referencefor an alignment between the reticle and the object, an irradiatingsection for irradiating light that transmits the reference mark andenters the projection optical system, and a fluid that has a refractiveindex of 1 or greater, and fills a space between the reference mark andthe irradiating section.

An exposure apparatus according to another aspect of the presentinvention includes a projection optical system for projecting a patternon a reticle onto an object, a reference mark that serves as a referencefor an alignment between the reticle and the object, and ananti-reflection member for preventing a total reflection of light thathas passed the reference mark and has not yet been received by thelight-receiving element.

An exposure apparatus according to another aspect of the presentinvention includes a projection optical system for projecting a patternon a reticle onto an object, a light-receiving element for receivinglight that transmits the reference mark, and an adjuster, arrangedbetween the reference mark and the light-receiving element, foradjusting an numerical aperture of the light.

An exposure method according to another aspect of the present inventionfor exposing a pattern on a reticle onto an object includes the step ofaligning the reticle and the object with each other by using lighthaving a numerical aperture of 1 or greater.

A device manufacturing method according to another aspect of the presentinvention includes the steps of exposing an object using the aboveexposure apparatus, and developing the object that has been exposed.

Other objects and further features of the present invention will becomereadily apparent from the following description of the preferredembodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a structure of an exposureapparatus according to one aspect of the present invention.

FIG. 2 is a plane view showing one exemplary wafer-side pattern formedon a W-side reference plate.

FIG. 3 is a graph showing the light intensity changes of the light thattransmits the wafer-side pattern and is detected by a light-receivingelement.

FIG. 4 is a schematic block diagram of a structure of an exposureapparatus according to another aspect of the present invention.

FIG. 5 is an enlarged view near the W-side reference plate of theexposure apparatus shown in FIG. 4.

FIG. 6 is an enlarged view near the W-side reference plate of theexposure apparatus shown in FIG. 4.

FIG. 7 is an enlarged view near the W-side reference plate of theexposure apparatus shown in FIG. 4.

FIG. 8 is a schematic block diagram of a structure of an exposureapparatus according to another aspect of the present invention.

FIG. 9 is an enlarged view near the W-side reference plate of theexposure apparatus shown in FIG. 8.

FIG. 10 is an enlarged view near the W-side reference plate in anon-immersion type exposure apparatus having a numerical aperture of 0.8or greater.

FIG. 11 is a flowchart for explaining a method for fabricating devices(semiconductor chips such as ICs, LSIs, and the like, LCDs, CCDs, etc.).

FIG. 12 is a detailed flowchart for Step 4 of wafer process shown inFIG. 11.

FIG. 13 is a graph showing an asymmetry of the light that transmits thewafer-side pattern detected by the light-receiving element.

FIG. 14 is a schematic block diagram showing a structure of an exposureapparatus that immerses the space between the sensor and the projectionoptical system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, a description will be givenof an exposure apparatus according to one aspect of the presentinvention. A like element in each figure is designated by the samereference numeral, and a duplicate description thereof will be omitted.Here, FIG. 1 is a schematic block diagram of the exposure apparatus 100according to one aspect of the present invention.

The exposure apparatus 100 includes, as shown in FIG. 1, an illuminationapparatus 110, a reticle stage 120, a projection optical system 130, awafer stage 140, a fluid 150, an off-axis optical system 160, and alight-receiving element 170. The exposure apparatus 100 is an immersiontype exposure apparatus that partially or locally immerses the finalsurface of the projection optical system 130 at the wafer W side in thefluid 150, and exposes a pattern on a reticle RC onto a wafer W via thefluid 150. The exposure apparatus 100 of the instant embodiment is astep-and-scan projection exposure apparatus, but the present inventionis applicable to a step-and-repeat exposure manner or other exposuremethods.

The exposure apparatus 100 provides the wafer stage 140 with awafer-side reference plate 142, forms a reference mark (or areticle-side pattern) 124 that is a reference for the alignment betweenthe reticle RC and the wafer W, and immerses the space between thewafer-side reference plate 142 and the projection optical system 130 inthe fluid 150. This configuration uses the projection optical system 130to establish an imaging relationship between the wafer-side pattern 144and the reference mark (or the reticle-side pattern) 124 on the reticleRC or the reticle-side reference plate 122. It is thus possible todetect a positional relationship between the reticle-side pattern 124and the wafer-side pattern 144 via the projection optical system 130 bymeans of the exposure light for calibration such as baselinemeasurements.

The illumination apparatus 110 illuminates the reticle RC on which acircuit pattern to be transferred is formed, and includes a light sourcesection and an illumination optical system.

The light source section includes a laser as a light source. The lasermay be pulsed laser such as an ArF excimer laser with a wavelength ofapproximately 193 nm, a KrF excimer laser with a wavelength ofapproximately 248 nm, a F₂ laser with a wavelength of approximately 157nm, etc. A kind of laser, the number of laser units, and a type of lightsource section is not limited.

The illumination optical system is an optical system that introduces thelight from the light source section to the reticle RC, and includes alens, a mirror, a light integrator, a stop, and the like. The lightintegrator may include a fly-eye lens or an integrator formed bystacking two sets of cylindrical lens array plates (or lenticularlenses), and be replaced with an optical rod or a diffractive element.The illumination optical system may use both on-axis light and off-axislight.

The reticle RC has a circuit pattern (or an image) to be transferred.The reticle RC is made, for example, of quartz and supported and drivenby the reticle stage 120. Diffracted light through the reticle RC isprojected onto the wafer W through the projection optical system 130.The reticle RC and wafer W are located in an optically conjugaterelationship. Since the exposure apparatus 100 is a step-and-scanexposure apparatus (or a scanner), it transfers a pattern on the reticleRC onto the wafer W by scanning the reticle RC and wafer W. When theexposure apparatus 100 is a step-and-repeat exposure apparatus (or astepper), it exposes while making still the reticle RC and wafer W.

The reticle stage 120 supports the reticle RC, is connected to a drivemechanism (not shown), and controls driving of the reticle RC. Thereticle stage 120 and the projection optical system 130 are provided ona barrel stool supported via a damper, for example, to the base frameplaced on the floor. The drive mechanism (not shown) includes a linearmotor and the like, and drives the reticle stage 120 in XY directions,thus moving the reticle RC.

A reticle-side reference plate (R-side reference plate) 122 is providedin a predetermined area near the reticle RC on the reticle stage so thatthe pattern surface of the R-side reference plate 122 is approximatelylevel with the pattern surface of the reticle RC. A plurality ofreticle-side patterns 124 for alignments are formed on the patternsurface of the R-side reference plate 122. Since the reticle-sidepattern 124 is similar to the wafer-side pattern 144, which will bedescribed later, a detailed description thereof will be omitted.

The projection optical system 130 serves to image diffracted light froma pattern on the reticle RC onto the wafer W. The projection opticalsystem 130 may use an optical system including plural lens elements, anoptical system including plural lens elements and at least one concavemirror (a catadioptric optical system), an optical system includingplural lens elements and at least one diffractive optical element suchas a kinoform, a full mirror type optical system, and so on. Anynecessary correction of the chromatic aberration may use plural lensunits made from glass materials having different dispersion values (Abbevalues), or arrange a diffractive optical element such that it dispersesin a direction opposite to that of the lens unit.

The wafer W is an object to be exposed, onto which a photoresist isapplied. The wafer W broadly covers a liquid crystal substrate and otherobjects to be exposed. The wafer W is supported by a wafer stage 140.

The wafer stage 140 supports the wafer W and controls driving of thewafer W. The wafer stage 140 moves the wafer W using a linear motor inthe XYZ directions. The reticle RC and wafer W are, for example, scannedsynchronously, and the positions of the reticle stage 120 and the waferstage 140 are monitored, for example, by a laser interferometer and thelike, so that both are driven at a constant speed ratio. The wafer stage140 is installed on a stage surface plate supported on the floor and thelike, for example, via a damper.

A wafer-side reference plate (W-side reference plate) 142 is provided ina predetermined area near the wafer W on the wafer stage 140 so that thepattern surface of the W-side reference plate 142 is approximately levelwith the top surface of the wafer W (or an imaging surface of theprojection optical system 130).

A plurality of wafer-side patterns 144 for the alignments are formed onthe pattern surface of the W-side reference plate 142. The wafer-sidepattern 144 is formed as a repetitive pattern of light shielding parts144 a and light transmitting parts 144 b as shown in FIG. 2, and theinstant embodiment makes a critical dimension, a pitch, etc. of thelight shielding part 144 a and light transmitting part 144 b differentfrom the reticle-side pattern 124 by a magnification of the projectionoptical system 130. Here, FIG. 2 is a plane view showing one exemplarywafer-side pattern 144 formed on the W-side reference plate 142.

The bottom surface of the projection optical system 130 is immersed inthe fluid 150. The fluid 150 selects its material that has a goodtransmittance to the wavelength of the exposure light, does notcontaminate the projection optical system 130, and matches the resistprocess. The fluid 150 selects a material having a refractive indexgreater than 1 so as to increase the NA of the projection optical system130. The coating to a refractive element (i.e., a lens) that has a finalsurface of the projection optical system 130 protects the element fromthe fluid 150.

As discussed above, the fluid 150 fills the space between the finalsurface of the projection optical system 130 and the wafer-side pattern144 on the W-side reference plate 142, and serves to establish animaging relationship between the reticle-side pattern 124 and thewafer-side pattern 144 via the projection optical system 130.

The exposure apparatus 100 includes an alignment mechanism for aligningthe reticle RC with the wafer W in order to expose a pattern on thereticle RC onto the wafer W. The alignment mechanism includes a waferalignment optical system, and a calibration system. The wafer alignmentoptical system uses an off-axis alignment optical system 160 differentfrom the projection optical system 130 to detect the alignment mark onthe wafer W (or the wafer-side pattern 144 on the W-side reference plate142). The calibration system detects, via the projection optical system130, a position of the wafer-side pattern 144 on the wafer W (or W-sidereference plate 142 on the wafer stage 140) relative to the reticle-sidepattern 124 on the reticle RC (or the R-side reference plate 122 on thereticle stage 120).

The off-axis alignment optical system 160 serves to detect a position ofthe wafer W, and includes an alignment light source (not shown), a fiber161, an illuminating section 162, an objective lens 163, a relay lens164, and an image pickup device 165.

The off-axis alignment optical system 160 introduces light that isemitted from the alignment light source and has a wavelength that is notused for the exposure, to the illuminating section 162 via the fiber161, and illuminates the alignment mark on the wafer W. The objectivelens 163 and the relay lens 164 enlarge the illuminated alignment mark,and the resultant light is imaged on the image pickup device 165, suchas a CCD. The off-axis alignment optical system 160 detects the positionof the wafer W by utilizing the fact that the image position on theimage pickup device 165 changes as the alignment mark's positionchanges. The alignment for the wafer W by the off-axis alignment opticalsystem 160 at a position different from the exposure position becomesinaccurate as the baseline or the relationship between the exposureposition and the alignment position changes due to the environmentalvariances.

For the alignment with higher precision than the baseline's stability,the calibration system is used to measure the baseline. According to thecalibration system, the illumination apparatus 110 illuminates, with theexposure light, the reticle-side pattern 124 on the R-side referenceplate 122 (or the reticle RC), which has a guaranteed relativepositional relationship with the reticle RC on the reticle stage 120.Then, the projection optical system 130 projects the reticle-sidepattern 124 onto the wafer-side pattern 144 on the W-side referenceplate 142 on the wafer stage 140. Since this embodiment immerses thespace between the projection optical system 130 and the wafer-sidepattern 144 (or the W-side reference plate 142) in the fluid 150,similar to the space between the projection optical system 130 and thewafer W, the reticle-side pattern 144 is successfully imaged onto thewafer-side pattern 144 on the wafer-side reference plate 142.

The light-receiving element 170 is provided at the side of the backsurface 142 b of the W-side reference plate 142 opposing to the surface,on which surface the wafer-side pattern 144 is formed. Thelight-receiving element 170 may be a light intensity sensor fordetecting the light intensity of the light that transmits the wafer-sidepattern 144. Alternatively, the light-receiving element 170 may be animage pickup device, such as a CCD, in the instant embodiment.

The reticle-side pattern 124 is projected, via the projection opticalsystem 130, onto the wafer-side pattern 144 (i.e., a repetitive patternof the light shielding parts 144 a and the light transmitting parts 144b, which is different from the reticle-side pattern by the magnificationof the projection optical system 130). While the wafer stage 140 ismoved in the X direction, the light-receiving element 170 detects thelight that transmits the wafer-side pattern 144 (or the W-side referenceplate 142). FIG. 3 is a graph showing the light intensity changes of thelight that transmits the wafer-side pattern 144 and is detected by alight-receiving element 170, where the ordinate axis is the lightintensity and the abscissa axis is the position of the wafer stage 140.It is understood from FIG. 3 that the light intensity becomes maximum ata position where the image of the reticle-side pattern 124 accords withthe position of the wafer-side pattern 144. This configuration preciselymeasures the exposure position of the reticle-side pattern 124 by theprojection optical system 130.

Next, the wafer stage 140 is driven, and a distance between the exposureposition (or reticle-side pattern 124) and the off-axis alignmentoptical system 160's position (or the baseline) is calculated by usingthe off-axis alignment optical system 160 and detecting a position ofthe wafer-side pattern 144 on the W-side reference plate 142. A patternon the W-side reference plate 142 detected by the off-axis alignmentoptical system 160 may be the wafer-side pattern 144 or another pattern,whose position is guaranteed relative to the wafer-side pattern 144.

Thus, the alignment between the reticle RC and the wafer W is availableby detecting the alignment mark on the wafer W using the off-axisalignment optical system 160 whose positional relationship with theexposure position has been calculated. In detecting the wafer-sidepattern 144 on the W-side reference plate 142 by using the off-axisalignment optical system 160, the space between the off-axis alignmentoptical system 160 and the wafer-side pattern 144 (or the W-sidereference plate 142) may be or may not be immersed in the fluid 150. Incase of immersion, it is preferable to immerse the space between theoff-axis alignment optical system 160 and the wafer W. In case of noimmersion, it is preferable not to immerse the space between theoff-axis alignment optical system 160 and the wafer W. In other words,it is preferable to detect a position of the W-side reference plate 142in the same state as that of a detection of the wafer W using theoff-axis alignment optical system 160.

The light-receiving element 170 can obtain the light intensity changesof the light that transmits the wafer-side pattern 144, even when thewafer stage 140 is driven in the optical-axis direction of theprojection optical system 130 (or the Z direction) while the calibrationsystem aligns the image of the reticle-side pattern 124 with thewafer-side pattern 144 in the XY directions. Since the light intensitychange becomes maximum at a (best focus) position at which thereticle-side pattern 124 focuses on the wafer-side pattern 144 (or theW-side reference plate 142), the focus position of the projectionoptical system 130 can be detected.

The aberration (or the imaging performance) of the projection opticalsystem 130 can be calculated by measuring the light intensity changes indetail when the wafer stage 140 is driven. For example, when theprojection optical system 130 has a spherical aberration, the lightintensity changes asymmetrically as the wafer stage 140 moves in the Zdirection, as shown in FIG. 13. As a result of the evaluation of thedegree of this asymmetry, the spherical aberration of the projectionoptical system 130 can be calculated. The evaluation of the asymmetry ofthe light intensity changes as the wafer stage 140 moves in the Z or Ydirection provides a coma.

It is possible to satisfactorily form an image of the reticle-sidepattern 124 onto the wafer-side pattern 144 and to provide highlyaccurate calibrations similar to the prior art (or in the manner similarto the prior art), by providing the W-side reference plate 142 on thewafer stage 140 and by immersing the space between the projectionoptical system 130 and the wafer-side pattern 144 (or the W-sidereference plate 142) in the fluid 150. An immersion holding plate LP maybe provided on the wafer stage 140 so as to maintain the immersion ofthe space between the W-side reference plate 142 and the projectionoptical system 130 by the fluid 150 equivalent to the immersion of thespace between the wafer W and the projection optical system 130. Theimmersion holding plate LP serves to fill the space between the wafer Wand the W-side reference plate 142, and is made of a member that makesthe pattern surface of the W-side reference plate 142 level with the topsurface of the wafer W. The W-side reference plate 142 is formed on thewafer stage 140 near the wafer W so that there is no clearance betweenthe wafer W and the W-side reference plate 142.

The exposure apparatus 100 provides the W-side reference plate 142 onthe wafer stage 140, and immerses the space between the projectionoptical system 130 and the W-side reference plate 142 in the fluid 150,establishes the imaging relationship between the reticle-side pattern144 and the wafer-side pattern 124, and provides highly accuratecalibration.

However, the exposure apparatus 100 includes an area A having arefractive index of 1, such as the air and vacuum, between the W-sidereference plate 142 and the light-receiving element 170. Therefore, whenthe light having an NA greater than 1 is used to image the reticle-sidepattern 124 on the R-side reference plate 122 on the wafer-side pattern144 on the W-side reference plate 142, the back surface 142 b of theW-side reference plate 142 totally reflects the light having an NAgreater than 1 and this light cannot enter the light-receiving element170, resulting in offsets in measurement values, the deterioratedmeasurement reproducibility, and incorrect measurement values. Inparticular, in detecting a (focus) position of the projection opticalsystem 130 by moving the W-side reference plate 142 in the optical-axisdirection of the projection optical system 130 (or the Z direction), thelight-receiving element 170 does not receive the light that has the highNA and is most sensitive to the focus changes, lowering the measuringprecision.

Accordingly, the exposure apparatus 100A shown in FIGS. 4 and 5immerses, in the fluid 180, not only the space between the patternsurface of the W-side reference plate 142 and the projection opticalsystem 130, but also the space between the back surface 142 b of theW-side reference plate 142 and the light-receiving element 170. Thefluid 180 selects its material so that it has a good transmittance tothe wavelength of the exposure light, does not contaminate the W-sidereference plate 142 and the light-receiving element 170, and possesses arefractive index greater than 1. The fluid 180 may be the same as ordifferent from the fluid 150 as long as the exposure light is nottotally reflected on the back surface 142 b of the W-side referenceplate 142. Here, FIG. 4 is a schematic block diagram of a structure ofthe exposure apparatus 100A according to another aspect of the presentinvention. FIG. 5 is an enlarged view near the W-side reference plate142 of the exposure apparatus 100A shown in FIG. 4.

An immersion of the space between the back surface 142 b of the w-sidedreference plate 142 and the light-receiving element 170 in the fluid 180that has a refractive index greater than 1 enables the light thattransmits the wafer-side pattern 144 to enter the light-receivingelement 170 without a total reflection on the back surface 142 b of theW-side reference plate 142, even when the projection optical system 130has an NA greater than 1. In other words, the light having a high NA canenter the light-receiving element 170. This configuration eliminates theoffset from the measurement value, maintains the measurementreproducibility, and obtains the correct measurement value. Inparticular, the focus position of the projection optical system 130 canbe detected with high precision.

It is conceivable to use water for the fluid (or the fluids 150 and 180)as an immersion material down to the wavelength of the ArF excimerlaser. However, as shown in FIGS. 4 and 5, the configuration that fillsthe space between the back surface 142 b of the W-side reference plate142 and the light-receiving element 170 (or which immerses thelight-receiving element 170 entirely in the fluid 180) with the fluid180 as the water is often very difficult because there are some electriccontacts around the light-receiving element 170.

Accordingly, one solution shown in FIG. 6 arranges a plane-convex lens190 is arranged between the back surface 142 b of the W-side referenceplate 142 and the light-receiving element 170, and immerses the spacebetween a plane 192 of the plane-convex lens 190 and the back surface142 b of the W-side reference plate 142 in the fluid 180. Theplane-convex lens 190 is made, for example, of a lens formed by cuttinga spherical lens or edgeless meniscus lens, and the plane 192 opposes tothe wafer-side pattern 144. FIG. 6 is an enlarged view near the W-sidereference plate 142 in the exposure apparatus 100A shown in FIG. 4.

This configuration enables the light that transmits the wafer-sidepattern 144 to enter the plane-convex lens 190 without a totalreflection on the back surface 142 b of the W-side reference plate 142.Since a curved surface 194 of the plane-convex lens 190 receivesapproximately perpendicular light by approximately according the radiusof curvature of the plane-convex lens 190 with the wafer-side pattern144 on the W-side reference plate 142, even the light having an NAgreater than 1 can enter the light-receiving element 170 without a totalreflection on the curved surface 194. It is possible to fill the gas,such as the air and inert gas, in the space around the light-receivingelement 170, i.e., between the plane-convex lens 190 and thelight-receiving element 170. When a distance between the plane 192 ofthe plane-convex lens 190 and the back surface 142 b of the W-sidereference plate 142 is made smaller than the wavelength of the incidentlight, the light that transmits the wafer-side pattern 144 is preventedfrom being totally reflected on the back surface 142 b of the W-sidereference plate 142.

As shown in FIG. 7, the light that transmits the wafer-side pattern 144and has an NA greater than 1 can be enter the light-receiving element170 by convexing the back surface 142 b of the W-side reference plate142. The curvature is set according to the NA of the light thattransmits the wafer-side pattern 144 and the refractive index of theW-side reference plate 142 so that no total reflection occurs on theback surface 142 b of the W-side reference plate 142 (or the convexsurface having the curvature). Here, FIG. 7 is an enlarged view near theW-sided reference plate 142 of the exposure apparatus 10A shown in FIG.4.

The above embodiment adopts the light intensity detecting method thatdetects the positional relationship between the reticle-side pattern 124and the wafer-side pattern 144 by arranging the light-receiving element170 at the side of the back surface 142 b of the W-side reference plate142 for the calibration system, and by detecting the light intensitychanges of the light that transmits the illuminated wafer-side pattern144. On the contrary, the following embodiment adopts the imagedetecting method that detects the positional relationship between thereticle-side pattern 124 and the wafer-side pattern 144 by using anoptical system to image the wafer-side pattern 144 and the reticle-sidepattern 124 on the image pickup device, such as a CCD.

As shown in FIG. 8, the exposure apparatus 200 having the calibrationsystem of the image detecting manner uses the optical system, such asthe objective lens 210 and the relay lens 220, to image the reticle-sidepattern 124 and the wafer-side pattern 144 on the image pickup device230, and detects the positional relationship between the reticle-sidepattern 124 and the wafer-side pattern 144, similar to the off-axisalignment optical system 160. The light source for the calibrationsystem according to the image detecting method preferably uses the samewavelength as that of the exposure light, and generally uses theexposure light source. Here, FIG. 8 is a schematic block diagram showinga structure of an exposure apparatus 200 according to one aspect of thepresent invention.

The light from the light source section in the illumination apparatus100 is introduced to the irradiation section 240 on the wafer stage 140via a fiber (not shown) so as to illuminate the wafer-side pattern 144on the W-side reference plate 142. The illuminated wafer-side pattern144 is enlarged by the projection optical system 130, the objective lens210, and the relay lens 220, and imaged on the image pickup device 230,such as a CCD. In addition to the objective lens 210 and the relay lens220, another optical system may be added to improve the enlargementmagnification.

The reticle-side pattern 124 on the R-side reference plate 122 (or thereticle RC) is illuminated using the light that transmits the wafer-sidepattern 144 on the W-side reference plate 142 and passes the projectionoptical system 130. The illuminated reticle-side pattern 124 is enlargedand imaged on the image pickup device 230 using the objective lens 210and the relay lens 220. Since this embodiment uses the exposure light,the reticle-side pattern 124 on the R-side reference plate 122 and thewafer-side pattern 144 on the W-side reference plate 142 have a similarimaging relationship to that for the exposure time. Therefore, the sameoptical system simultaneously detects the reticle-side pattern 124 andthe wafer-side pattern 144. Thereby, an exposure position on thereticle-side pattern 124 can be precisely detected without consideringthe influence of errors of the optical system, etc.

This embodiment fills, with the fluid 180 as shown in FIG. 9, the spacebetween the back surface 142 b of the W-side reference plate 142 (or thewafer-side pattern 144) and the irradiating section 240 that irradiatesthe light having the same wavelength as that of the exposure light. Thisconfiguration enables, for example, the light having an NA ofsubstantially 1.35 to enter the projection optical system 130, where therefractive index of the fluid 180 is 1.5, and the NA of the lightirradiated from the irradiating section 240 is 0.9 in the air. In otherwords, an immersion of the space between the back surface 142 b of theW-side reference plate 142 and the irradiating part 240 in the fluid 180enables the light having an NA greater than 1 to enter the projectionoptical system 130, and the reticle-side pattern 142 and the wafer-sidepattern 144 to be aligned with each other in the image detecting method.The instant embodiment is not limited to the image detecting method, butis effective to all the methods that make the light having an NA greaterthan 1 incident upon the projection optical system 130 from a side ofthe wafer stage 140. Here, FIG. 9 is an enlarged view near the W-sidereference plate 142 of the exposure apparatus 200 shown in FIG. 8.

As discussed above, the immersion type exposure apparatus immerses thespace between the projection optical system and the W-side referenceplate and successfully forms an image of the reticle-side pattern on theW-side reference plate (or the wafer-side pattern), realizing acalibration that is as precise as the non-immersion type exposureapparatus. An immersion of the space between the back surface of theW-side reference plate and the light-receiving element enables the lightthat transmits the wafer-side pattern to completely enter thelight-receiving element without the total reflection on the back surfaceof the W-side reference plate even if the NA of the projection opticalsystem exceeds 1. Therefore, a positional relationship between thereticle-side pattern and the wafer-side pattern can be detectedprecisely. Other configurations, such as an arrangement of aplane-convex lens between the W-side reference plate and thelight-receiving element, an immersion of the space between the backsurface of the W-sided reference plate and the plane-convex lens, and anadjustment of a distance between the back surface of the W-sidereference plate and the plane-convex lens to a distance below thewavelength of the light, also enable the light that transmits thewafer-side pattern to completely enter the light-receiving elementwithout the total reflection on the back surface of the W-side referenceplate even if the NA of the projection optical system exceeds 1. Animmersion of the space between the back surface of the W-side referenceplate and the irradiating section enables the light having an NA greaterthan 1 to enter the projection optical system from the wafer side andthe reticle-side pattern and the wafer-side pattern to be aligned witheach other in accordance with the image detecting method. It may be saidthat the above exposure apparatus includes an adjusting means, such asthe fluid and plane-convex lens, for adjusting the NA of the lightbetween the W-side reference plate and the light-receiving element.

In exposure, light emitted from an illumination apparatus 110, forexample, Koehler-illuminates the reticle RC. The light that has passedthe reticle RC and reflects the reticle pattern forms an image on thewafer W through the projection optical system 130. Since the exposureapparatuses 100, 100A and 200 can realize highly precise calibration andaccurately align the reticle RC with the wafer W, the exposure apparatus1 can provide higher quality devices (such as semiconductor devices, LCDdevices, image pick-up devices (such as CCDs), and thin film magneticheads) than the conventional.

A non-immersion type exposure apparatus is also required to have aprojection optical system with a higher NA, e.g., an NA of 0.9 orgreater, along with the demands for finer processing to semiconductors.On the other hand, the high NA of the projection optical system requiresa light-receiving element having a large light receiving area forcalibrations in the light intensity detecting method. This isdisadvantageous because the wafer stage becomes large when thelight-receiving element having the large light receiving area isprovided on the wafer stage. Another problem occurs when the light thathas a high NA and is most sensitive to changes of the focus and imagingperformance (or aberration) of the projection optical system isreflected on the back surface of the W-side reference plate and thus isnot incident upon the light-receiving element.

Accordingly, the space between the back surface 142 b of the W-sidereference plate 142 (or the wafer-side pattern 144) and thelight-receiving element 170 is immersed in the fluid 180 having arefractive index greater than 1, as shown in FIG. 10, in a non-immersiontype exposure apparatus that includes a projection optical system 130having an NA of 0.8 or greater, and does not immerse the space betweenthe projection optical system 130 and the wafer W. The fluid 180preferably has a refractive index equal to that of the W-side referenceplate 142. An immersion of the space between the back surface 142 b ofthe W-side reference plate 142 and the light-receiving element 170 inthe fluid 180 can reduce a diameter of the light that transmits thewafer-side pattern 144 and enters the light-receiving element 170. Forexample, where the thickness of the substrate is 3.0 mm, the refractiveindex is 1.5, a distance between the back surface of the substrate andthe sensor is 2 mm, the refractive index of the fluid is 1.5, and the NAof the projection optical system is 0.8, the effective diameter on thesensor surface is Φ9.1 mm if the space between the back surface and thesensor is filled with the air, and Φ6.3 mm if the space between the backsurface and the sensor is immersed. Therefore, the effective diameter isreduced down to about 70%. Here, FIG. 10 is an enlarged view near theW-side reference plate in a non-immersion type exposure apparatus havingan NA of 0.8 or greater.

A description will be given of another embodiment of the presentinvention. While the above embodiment forms the W-side reference plate142 on the wafer stage 140, this embodiment immerses the space betweenthe sensor 170 and the projection optical system 130 in the fluid 150 asshown in FIG. 14 without forming the W-side reference plate 142. Thisconfiguration enables the immersion type exposure apparatus to use thesensor 170 on the wafer stage 140 to measure the light intensity on thewafer stage, and the transmittance of the projection optical system 130.It is also possible to arrange a sensor that includes devices arrangedin an array shape, such as a CCD, near the image surface, and to measurethe position of the light projected on the sensor for use with thealignment. As shown in FIG. 14, a CCD may be arranged at a defocusposition in order to simply observe a pupil surface of the projectionoptical system.

For example, when there is the air between the W-side reference plate142 and the light-receiving element 170, the light refracts and divergeson the back surface 142 b of the W-side reference plate 142, increasingthe effective diameter. On the other hand, as shown in FIG. 10, when thefluid 180 is having the same refractive index as that of the W-sidereference plate 142 immerses the space between the back surface 142 b ofthe W-side reference plate 142 and the light-receiving element 170, asshown in FIG. 10, the light does not refract on the back surface 142 bof the W-side reference plate 142, and the diameter of the incidentlight upon the light-receiving element 170 can be made small. Inaddition, no reflection occurs on the back surface 142 b of the W-sidereference plate 142, the light can enter the light-receiving element 170without losses of the reflections of the light having a large NA. Asdiscussed above, if it is difficult to immerse the light-receivingelement 170 itself in the fluid 180, use of the plane-convex lens or theshaping the back surface 142 b of the W-side reference plate 142 into aconvex shape would provide similar effects.

The above non-immersion type exposure apparatus can immerse the spacebetween the W-side reference plate and the light-receiving element,reduce the size of the light-receiving element by arranging theplane-convex lens, and detect light-intensity changes while restrainingthe influence of the reflectance on the back surface of the W-sidedreference plate.

Referring to FIGS. 11 and 12, a description will now be given of anembodiment of a device fabricating method using the above exposureapparatus. FIG. 11 is a flowchart for explaining a fabrication ofdevices (i.e., semiconductor chips such as IC and LSI, LCDs, CCDs,etc.). Here, a description will be given of a fabrication of asemiconductor chip as an example. Step 1 (circuit design) designs asemiconductor device circuit. Step 2 (mask fabrication) forms a maskhaving a designed circuit pattern. Step 3 (wafer preparation)manufactures a wafer using materials such as silicon. Step 4 (waferprocess), which is referred to as a pretreatment, forms actual circuitryon the wafer through photolithography using the mask and wafer. Step 5(assembly), which is also referred to as a post-treatment, forms into asemiconductor chip the wafer formed in Step 4 and includes an assemblystep (e.g., dicing, bonding), a packaging step (chip sealing), and thelike. Step 6 (inspection) performs various tests for the semiconductordevice made in Step 5, such as a validity test and a durability test.Through these steps, a semiconductor device is finished and shipped(Step 7).

FIG. 12 is a detailed flowchart of the wafer process in Step 4. Step 11(oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms aninsulating film on the wafer's surface. Step 13 (electrode formation)forms electrodes on the wafer by vapor disposition and the like. Step 14(ion implantation) implants ions into the wafer. Step 15 (resistprocess) applies a photosensitive material onto the wafer. Step 16(exposure) uses the exposure apparatus 100 to expose a circuit patternon the mask onto the wafer. Step 17 (development) develops the exposedwafer. Step 18 (etching) etches parts other than a developed resistimage. Step 19 (resist stripping) removes disused resist after etching.These steps are repeated, and multilayer circuit patterns are formed onthe wafer. The device manufacture method of the present invention maymanufacture higher quality devices than the conventional one. Thus, thedevice manufacturing method using the inventive lithography, andresultant devices themselves as intermediate and finished products alsoconstitute one aspect of the present invention. Such devices includesemiconductor chips like an LSI and VLSI, CCDs, LCDs, magnetic sensors,thin film magnetic heads, and the like.

Thus, the present invention can provide an exposure apparatus having aprojection optical system that has a high NA (such as an immersion typeor 1<NA), and realizes a precise alignment and an exposure with superiorresolution without increasing the size of the apparatus.

Further, the present invention is not limited to these preferredembodiments, and various modifications and changes may be made in thepresent invention without departing from the spirit and scope thereof.For example, the present invention is applicable, for example, to use ofthe light-receiving element provided on the wafer stage to measure thelight intensity on the wafer stage and the transmittance of theprojection optical system.

This application claims foreign priority benefits based on JapanesePatent Application No. 2003-409881, filed on Dec. 9, 2003, which ishereby incorporated by reference herein in its entirety as if fully setforth herein.

1. An exposure apparatus comprising: a projection optical system forprojecting a pattern on a reticle onto an object to be exposed; areference mark that serves as a reference for an alignment between thereticle and the object; a first fluid that has a refractive index of 1or greater, and fills a space between at least part of said projectionoptical system and the object and a space between at least part of saidprojection optical system and the reference mark; and an alignmentmechanism for aligning the object by using said projection opticalsystem and the first fluid.
 2. An exposure apparatus according to claim1, further comprising: a stage for mounting the object; and a referenceplate mounted on said stage and made of a transparent material thattransmits light, wherein said reference mark is provided on thereference plate.
 3. An exposure apparatus according to claim 2, whereinsaid alignment mechanism includes a light-receiving element provided onsaid reference plate at a back of a surface on which said reference markis formed, the light-receiving element receiving light that transmitsthe reference mark, wherein said exposure apparatus further comprises asecond fluid that has a refractive index of 1 or greater, and fills aspace between said reference mark and the light-receiving element.
 4. Anexposure apparatus according to claim 3, wherein said alignmentmechanism further includes a plane-convex lens provided between saidreference mark and the light-receiving element, the plane-convex lenshaving a plane opposing to the back of said reference plate, wherein thesecond fluid fills a space between said reference mark and theplane-convex lens.
 5. An exposure apparatus according to claim 2,wherein said alignment mechanism includes a light-receiving elementprovided on said reference plate at a back of a surface on which saidreference mark is formed, the light-receiving element receiving lightthat transmits the reference mark, wherein the back of said referenceplate has a convex shape having a curvature that does not cause a totalreflection of the light.
 6. An exposure apparatus according to claim 1,wherein said alignment mechanism has a plane-convex lens having a planeopposing to a back of a surface of said reference plate, on whichsurface said reference mark is formed, the plane being spaced from theback by a distance so that light that transmits the reference mark isnot totally reflected on the back of said reference plate.
 7. Anexposure apparatus according to claim 5, wherein the distance is smallerthan the wavelength of the light.
 8. An exposure apparatus according toclaim 1, wherein said alignment mechanism includes a light-receivingelement for receiving light that transmits said reference mark, whereinsaid exposure apparatus further comprises a second fluid that fills aspace between the reference mark and the light-receiving element, andhas a refractive index of 1 or greater.
 9. An exposure apparatusaccording to claim 1, wherein said alignment mechanism includes anirradiating section for irradiating light that transmits said referencemark and enters said projection optical system, wherein said exposureapparatus further comprises a second fluid that fills a space betweensaid reference mark and the irradiating section, and has a refractiveindex of 1 or greater.
 10. An exposure apparatus according to claim 2,wherein said alignment mechanism includes an irradiating sectionarranged at a back of a surface of said reference plate, on whichsurface said reference mark is formed, wherein said exposure apparatusfurther comprises a second fluid that immerses a space between thereference mark and the irradiating section, and has a refractive indexof 1 or greater.
 11. An exposure apparatus comprising: a projectionoptical system for projecting a pattern on a reticle onto an object; areference mark that serves as a reference for an alignment between thereticle and the object; a light-receiving element for receiving lightthat transmits said reference mark; and a fluid that has a refractiveindex of 1 or greater, and fills a space between said reference mark andsaid light-receiving element.
 12. An exposure apparatus according toclaim 11, further comprising: a stage for mounting the object; and areference plate mounted on said stage and made of a transparent materialthat transmits light, wherein said reference mark is provided on thereference plate.
 13. An exposure apparatus according to claim 12,wherein said alignment mechanism further includes a plane-convex lensprovided between said reference mark and the light-receiving element,the plane-convex lens having a plane opposing to the back of saidreference plate, wherein the fluid fills a space between said referencemark and the plane-convex lens.
 14. An exposure apparatus according toclaim 11, wherein said projection optical system has a numericalaperture of 0.8 or greater.
 15. An exposure apparatus comprising: aprojection optical system for projecting a pattern on a reticle onto anobject; a reference mark that serves as a reference for an alignmentbetween the reticle and the object; an irradiating section forirradiating light that transmits said reference mark and enters saidprojection optical system; and a fluid that has a refractive index of 1or greater, and fills a space between said reference mark and saidirradiating section.
 16. An exposure apparatus according to claim 15,further comprising: a stage for mounting the object; and a referenceplate mounted on said stage and made of a transparent material thattransmits light, wherein said reference mark is provided on thereference plate.
 17. An exposure apparatus according to claim 16,wherein said alignment mechanism further includes a plane-convex lensprovided between said reference mark and the light-receiving element,the plane-convex lens having a plane opposing to the back of saidreference plate, wherein the fluid fills a space between said referencemark and the plane-convex lens.
 18. An exposure apparatus comprising: aprojection optical system for projecting a pattern on a reticle onto anobject; a reference mark that serves as a reference for an alignmentbetween the reticle and the object; and an anti-reflection member forpreventing a total reflection of light that has passed said referencemark and has not yet been received by said light-receiving element. 19.An exposure apparatus according to claim 18, further comprising: a stagefor mounting the object; and a reference plate mounted on said stage andmade of a transparent material that transmits light, wherein saidreference mark is provided on the reference plate, wherein saidantireflection member has a convex shape that has a curvature that doesnot cause a total reflection of the light, and is formed on a back of asurface of said reference plate, on which surface said reference mark isformed.
 20. An exposure apparatus according to claim 18, furthercomprising: a stage for mounting the object; and a reference platemounted on said stage and made of a transparent material that transmitslight, wherein said reference mark is provided on the reference plate,wherein said antireflection member includes a plane-convex lens that hasa plane that opposes a back of a surface of the reference plate, onwhich surface said reference mark is formed, and is spaced from the backby a distance so that light that passes the reference mark is nottotally reflected on the back of the reference plate.
 21. An exposureapparatus according to claim 18, wherein the light-receiving element isa light intensity sensor for detecting a light intensity change of thelight.
 22. An exposure apparatus according to claim 21, furthercomprising a calculating section for calculating a positionalrelationship between the reticle and the object in an optical-axisdirection of said projection optical system, based on the lightintensity change detected by the light intensity sensor.
 23. An exposureapparatus according to claim 21, further comprising a calculatingsection for calculating an aberration of said projection optical systembased on the light intensity change detected by said light intensitysensor.
 24. An exposure apparatus comprising: a projection opticalsystem for projecting a pattern on a reticle onto an object; alight-receiving element for receiving light that transmits saidreference mark; and an adjuster, arranged between said reference markand the light-receiving element, for adjusting an numerical aperture ofthe light.
 25. An exposure apparatus according to claim 24, wherein saidadjuster has a fluid that has a refractive index of 1 or greater, andfills a space between said reference mark and said light-receivingelement.
 26. An exposure apparatus according to claim 24, wherein saidexposure apparatus is an immersion type exposure apparatus that immersesat least part of said projection optical system in a fluid that has arefractive index of 1 or greater.
 27. An exposure method for exposing apattern on a reticle onto an object, said exposure method comprising thestep of: aligning the reticle and the object with each other by usinglight having a numerical aperture of 1 or greater.
 28. An exposuremethod according to claim 27, wherein at least part of the projectionoptical system is filled with the fluid having a refractive index of 1or greater.
 29. A device manufacturing method comprising the steps of:exposing an object using an exposure apparatus according to claim 1; anddeveloping the object that has been exposed.